This disclosure relates generally to the field of mapping induced fractures in subsurface formations, more specifically, the disclosure relates to method for identifying orientation of fractures induced, for example, by hydraulic fracturing using passive seismic signals detected above the formation in which the fractures are induced.
Passive seismic-emission tomography is a technique that is used for, among other purposes, determining the hypocenter (i.e., place and time of origin) of microearthquakes such as formation fracturing that occurs in subsurface rock formations. Such microeathquakes may be naturally occurring or may be induced, for example, by pumping fluid into formations at sufficient pressure to cause failure, i.e., fracturing of the formation. In the latter case, it is useful to be able to determine progression of the fluid front as the fluid is pumped into the formations. One technique for performing such fluid front determination during fracture pumping is described in U.S. Pat. No. 7,663,970 issued to Duncan et al. incorporated herein by reference in its entirety. The technique described in the Duncan et al. '970 patent may be used to determine hypocenters of microseismic events (or microearthquakes) caused by failure of the subsurface rock formations as hydraulic fracturing fluid is pumped into the formations.
What is needed is a technique that can be used to determine orientation of fracture planes of such induced fractures.